The invention relates to retroreflective articles and other articles useful for various applications, such as reflective footwear, reflective apparel, and retroreflective signage and pavement markings.
Plasticized polyvinyl chloride (PVC) films and tapes are conventionally used for a wide variety of retroreflective article applications including reflective footwear, reflective apparel, and retroreflective signage and pavement markings. PVC has many advantages that have caused it to become a material of choice in such applications. For example, plasticized PVC films can readily be applied to many irregular surfaces. Thus a PVC-based retroreflective sheet can be heated slightly above room temperature and stretched over rivets and into small indentations such as may be present on the substrates to which such retroreflective sheets may be applied. Many materials that have been tried as substitutes for PVC have been found to undergo necking or other non-affine deformation when stretched, thus rendering such materials unsuitable for applications in which non-uniform distortion during stretching would be unacceptable.
Plasticizers are typically employed in PVC films in order to make the films more flexible and more stretchable. However, PVC plasticizers can degrade the performance of adjacent adhesive layers, reducing the adherence of a retroreflective sheet to a substrate. PVC plasticizers can also migrate into and thereby degrade the performance of retroreflective sheeting.
In addition, there is growing concern, particularly in European and Japanese markets, about the environmental impact of land filling or incinerating PVC materials. PVC has only limited recycling utility.
A variety of stiff, relatively high modulus packaging films (e.g., twist films for candy wrapping) have been made from isotactic (crystalline) polypropylene and hydrocarbon resins, including the films described in U.S. Pat. Nos. 3,278,646; 3,361,849; 3,666,836; 4,032,493; 4,289,831; 4,394,235; 5,091,237; 5,128,183; 5,212,009; 5,213,744; 5,246,659; 5,290,635; 5,451,455; 5,543,223; 5,560,948 and 5,777,055; and in European Patent Specification No. EP 0 681 914 B1. U.S. Pat. No. 5,085,943 also describes a twist film made from polypropylene and hydrocarbon resin, the film being said to have increased stiffness. PCT International Application Nos. WO 98/38041, WO 99/2331 and WO 99/51432 describe multilayer films having a core layer that contains isotactic propylene and various modifiers including a tactic polypropylene. European Patent Specification No. EP 0 763 422 A1 refers to various multilayer films containing low-modulus polypropylene in an interior layer, and refers to but does not exemplify film layers containing a blend of low-modulus polypropylene and hydrocarbon resin.
Fibers made from isotactic polypropylene and hydrocarbon resins are described in, for example, U.S. Pat. Nos. 4,115,620 and 5,171,628, and in European Patent Application No. 0 399 792 A3.
Hot melt adhesives, sealants and other compositions containing, inter alia, atactic (amorphous) polypropylene and various hydrocarbon resins are described in many references, including U.S. Pat. Nos. 3,341,626; 3,983,206; 4,048,376; 4,081,415 and 4,279,659. U.S. Pat. No. 4,999,231 describes cast hot melt adhesive films for use on carpet backing, wherein the films contain, inter alia, atactic polypropylene, hydrocarbon resin and calcium carbonate filler. U.S. Pat. No. 4,692,370 describes a fibrous coating made from blown strands of a hot melt material made from, inter alia, atactic polypropylene and a polyterpene resin. U.S. Pat. Nos. 5,047,462; 5,248,719 and 5,472,764 describe coating compositions containing, inter alia, various atactic copolymers and hydrocarbon resin. European Patent Application No. 0 557 593 A2 describes packaging films containing, inter alia, a hydrocarbon resin and a wax. Atactic polypropylene is mentioned as one possible wax.
PVC replacement films are described in, for example, U.S. Pat. Nos. 5,112,674; 5,132,074 and 5,460,861.
The present invention provides, in one aspect, a retroreflective article comprising a plurality of retroreflective elements and a film comprising a blend of polyolefin and hydrocarbon resin, wherein the polyolefin is semicrystalline and has a suitable degree of crystallinity and molecular weight, or the polyolefin is amorphous and has sufficiently high molecular weight, and sufficient hydrocarbon resin is present in the blend, so that the film is substantially vinyl-like. In some embodiments of the invention, the film is elastomeric, and in other embodiments the film is non-elastomeric. In further embodiments of the invention, the film is conformable, drapable or affinely deformable by hand. In yet further embodiments, the films are oriented sufficiently so that the film has a deformation index that is less than about 1.1.
In another aspect, the invention provides retroreflective articles comprising a plurality of retroreflective elements and a multilayer film comprising a core of the above-mentioned blend and one or more additional layers made of a different material.
The invention also provides a method for making a retroreflective article comprising the steps of providing a retroreflective member having a plurality of retroreflective elements; extruding a film comprising a layer of the above-mentioned blend; and attaching the film to the retroreflective member.
The invention provides retroreflective articles having vinyl-like features and behavior. The retroreflective articles and method of the invention can be tailored to provide specific desired physical properties at room temperature (20xc2x0 C.) and at elevated temperatures, and can provide workable substitutes for retroreflective articles employing existing plasticized PVC films. At present raw material pricing, the invention enables a desirable reduction in raw material cost compared to many PVC films.